Term Discovery metric.
In its simplest form, spoken term discovery consist in finding clusters or pairs of speech segments that have the same transcription from unsegmented audio. It is evaluated by the NED/COV as introduced in the zero speech challenges [1]}. For each discovered pair, the Normalised Edit Distance (NED) is computed as the edit distance normalised by the length of the loangest item in the pair. The coverage (COV) is given by the proportion of phonemes in the corpus that is covered by least one speech sequence from the sets of pairs. There is typically a tradeoff between these two measures: low NED systems have typically low COV, and high COV have high NED.
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